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The 35W4 is a half wave rectifier designed for use with a 150 mA heater chain. The heater is tapped at about 7.5v and the tap can be used to feed a scale light.

If the radio has a scale lamp then the mains live feeds into the light bulb and the pin 4 end of the heater. The other end of the bulb, and the heater tap (pin 6), connect to the rectifier anode. The other end of the heater, pin 3, connects to rest of the series heater chain and carries 0.15A. The section with the bulb across it carries the full mains current, i.e. 0.1 A AC plus the 50Hz current pulses into the anode of the rectifier. Once the set has warmed up there is about 0.3A RMS which splits into 0.15A for the bulb and 0.15A for the pin 4 to 6 section of the heater.

The reason for this arrangement is that if the bulb was put in the series heater chain it would blow at switch-on because of the high surge current into the cold heaters. This arrangement means the bulb is shunted by a cold heater and so protected. The HT current comes up slowly so the lamp current ramps up gently too. This valve line-up, called the 'All American Five', resulted in a very cheap radio. No mains transformer, no series dropper resistor in the heater chain (the heaters add up to about 120v), no thermistor to protect the bulb. The drawback is that if the bulb blows then the 35CW4 won't last many months before it blows too.

The protective minimum series resistance has to be 120 Ohms and the rectifier will feed a reservoir capacitor of 40 μF maximum.

The anode plates are turned out at the ends revealing the bright interior surface.

The two parts of the anode are stitched together.

The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 58 mm tall.

References: Data-sheet, ³⁰⁰² & ¹⁰⁴⁰. Type 35W4 was first introduced in 1946. See also 1946 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.